In the above technical field, patent literature 1 discloses a technique in which an FTL (Flash Translation Layer) in a controller in an SSD (Solid State Drive) sequentially stores data in pages on a page basis in a write-once manner to avoid page save processing that is performed when updating data in a NAND flash memory (to be referred to as a NAND flash hereinafter). Patent literature 2 discloses a technique of adding a free area by estimating fragmentation based on the number of data extents.
Non-patent literature 1 discloses a technique of preventing, from increasing, the load of GC (Garbage Collection) of collecting a memory area storing data that has become unnecessary due to update or the like in order for an SSD to continuously store write data from a host computer in a write-once manner. Non-patent literature 1 describes a method of reducing the load of GC by adding information called the same stream ID to each set of data having the same property with respect to a write command from the host computer, selecting a storage destination block of the NAND flash in the SSD based on the stream ID, and storing the write data so that the update timings of data in each block are close to each other.